Currently, liquid crystal display devices are used widely in electronic apparatuses such as a monitor, a projector, a mobile phone and a Personal Digital Assistant (hereinafter, also referred to as a “PDA”) Such liquid crystal display devices are classified into reflective, transmissive, and transflective (semi-transmissive) types. The reflective liquid crystal display device is configured to obtain display light by guiding surrounding light to the inside of a liquid crystal display panel and reflecting this light by a reflective member. Furthermore, the transmissive liquid crystal display device is configured to obtain display light by guiding light from a light source (hereinafter, also referred to as a “backlight”) arranged on the back surface side of a liquid crystal display panel and emitting the light to the outside through the panel.
According to the transflective liquid crystal display device, transmissive display using light from the backlight is mainly observed under relatively dark environments such as indoor environment. Under relatively bright environments such as outdoor environment, reflective display using surrounding light is mainly observed. As a result, the transflective liquid crystal display device can perform display with a high contrast ratio regardless of surrounding brightness. That is, the transflective liquid crystal display device can perform display under all environments regardless of indoor and outdoor environments, and therefore such a device has been often equipped with mobile devices such as a cellular phone, a PDA, and a digital camera.
According to such a transflective liquid crystal display device, the liquid crystal panel has two different display regions: a reflective region; and a transmissive region. In the transmissive region, light from the backlight passes through a liquid crystal layer and a color filter only one time and then the light is emitted to the outside. In the reflective region, surrounding light passes through the color filter and the liquid crystal layer, and the light is reflected by a reflective member and further passes through the liquid crystal layer and the color filter again. Then, the light is emitted to the outside. Thus, the transmissive region and the reflective region use different light sources, that is, backlight and surrounding light, thereby generating display light. In addition, a color reproduction range in the transmissive display is obtained by causing light to enter the color filter only one time. A color reproduction range in the reflective display is obtained by causing light to enter the color filter twice.
A color filter used in a conventional liquid crystal display device is composed of filters having three primary colors of red, green, and blue. A color of light emitted from each color filter is expressed by additive color mixture of three primary colors of red, green, and blue. However, by using only these three primary colors, the color reproduction range is limited. Therefore, not all colors which can be recognized by human eyes can be expressed. Four or more color filters having different colors have been proposed in order to extend the color reproduction range and improve use efficiency of light. For example, the Patent Document 1 discloses a color filter including four colors consisting of yellow in addition to the three primary colors of red, green, and blue (hereinafter, also referred to as “four filters having different colors”). With respect to these four colors, blue and yellow are in a complementary color relationship, and red and green, and blue and yellow are pairs of opposite colors based on human visual characteristics.
White balance is mentioned as one of important display performances of the display device. This white balance is a color tone of white displayed by a display device, and mainly determined by a color tone of a light source and a configuration of a color filter. This white balance is often expressed as a color temperature (an absolute temperature of a black body having the same or almost the same chromaticity as a chromaticity of a certain light) quantitatively, and generally, a display for displaying TV images and the like needs a color temperature of 6500 K or more.
If the four filters having different colors are used as the color filter of the liquid crystal display device, the color reproduction range can be extended or the luminance can be improved. However, the white balance is significantly affected. For example, in a liquid crystal display device including a light source which corresponds spectral characteristics of filters having three primary colors, if four filters having different colors are used instead of the filters having three primary colors, the color temperature of the color filter is reduced, and thereby the white balance is shifted and white displayed by the display device becomes yellowish white.
The white balance in the transmissive display can be improved by adjusting the color tone of the light source in the backlight because the backlight is used as the light source. In the reflective display using surrounding light as the light source, however, it is difficult to improve the white balance by way of the light source. Even if the white balance in the transmissive display is improved, a large difference in white balance is generated between the transmissive display and the reflective display.
A method of previously adjusting the configuration of the four filters having different colors, thereby obtaining an optimal white balance in the reflective display, is mentioned. For example, a method of extremely decreasing the thickness of the blue filter, thereby increasing contribution of blue that is a complementary color of yellow, is mentioned. However, even if the thickness of the blue filter is reduced, white free from a yellow tinge is not obtained. Further, if such a design modification is performed, a color purity of blue is reduced. As a result, a large difference is generated between a display color and a color obtained using the three filters having different colors in accordance with NTSC (National Television System Committee) standard.
[Patent Document 1]
Japanese Kokai Publication No. 2001-209047